Conventionally, as a valve apparatus for a internal combustion engine, there is known one in which an inlet valve and an exhaust valve are directly driven to open or close by an electromagnetic actuator. The valve driven in this manner is referred to as a direct-acting valve.
As shown by a curve A in FIG. 6, the drive unit for this direct-acting valve applies, for example, a positive current to the electromagnetic actuator, to move the valve in the opening direction by a specific distance, and applies a negative current to the electromagnetic actuator, to move the valve in the closing direction.
However, in the conventional drive unit for the direct-acting valve, there are the following problems that need to be given attention.
That is, when the valve is closed, as shown by a curve B in FIG. 6, since the valve is shifted at once from the top end position of the valve stroke to the closing position, the valve is shifted to the closing position without deceleration.
When the valve is shifted to the closing position without deceleration, impulsive sound occurs when the valve is seated on a valve seat, causing noise.
Particularly, when the internal combustion engine is in the idling state, or in a state of low revolution speed, the noise when the valve seats becomes noticeable.
The present invention has been achieved in order to solve the above problems. It is an object of the present invention to provide a drive unit for a direct-acting valve for internal combustion engines that can result in a quiet internal combustion engine with noise suppressed.